A multitude of devices are known for which an electrical and mechanical coupling between a conductive lead and an electronic component must be established. For example, implantable medical devices such as cardiac pacemakers, cardioverters, defibrillators, neural stimulators, and the like, must be electrically and mechanically connected to one end of an electrical lead. In the case of an implantable medical device, there are particularly stringent design criteria with regard to the mechanical and electrical properties of the lead connection (i.e., the connection between a conductive lead and the device itself). In particular, the lead connection for an implantable device should preferably be highly reliable, both from a mechanical and from an electrical point of view. Any physical structure used in an implantable device lead connection should be small, light-weight, and biologically inert. A lead connection should preferably be capable of withstanding repeated flexing of the lead with respect to the device itself; this consideration is one reason that implantable leads are frequently of a coiled conductor type. Also, the lead connection should be strong enough to resist disconnection due to the various forces that may be exerted on the lead connection when implanted in a human body. Furthermore, since the implantation of a medical device is a delicate surgical process, the lead connection should be relatively simple to effectuate in the surgical environment.
Implanted medical devices such as pacemakers are battery-powered electronic devices which are susceptible to breakage, failure, or battery depletion. Thus, these devices may occasionally need to be explanted and/or replaced. Often, though, a lead associated with a device need not be removed along with the device. The previously implanted lead may be functioning adequately and may have even become ingrown within human tissue, making lead removal undesirable. Consequently, a further preferable feature of a lead connection for an implantable pulse generator is that it should allow for disconnection without damage to either the lead or the generator, in order that it may be removed and/or replaced without removal or replacement of the lead.
One prevalent means in the prior art for establishing the electrical and mechanical connection between a lead and an implantable pulse generator has been to provide a connector with molded-in connector blocks containing set screws. A terminal pin provided at the terminal end of the lead is received in a terminal receptacle in the connector, and the lead is then secured in place by tightening the set screws, which may also provide the requisite electrical contact between the lead conductor and the pacemaker's hermetic feedthrough elements.
With conventional connector and set screw lead connecting arrangements, proper tightening of the set screws is of critical importance. Over-torquing of a set screw can cause stripping of the set-screw threads or damage to the lead terminal or lead conductor. On the other hand, under-torquing of the set screw can lead to post-implant problems, since the lead terminal may become disengaged from the connector receptacle. In some cases, therefore, a specially designed set-screw driver or other tool may be provided as a means to ensure proper tightening. For instance, the tool may be designed to "break away" or flex after a proper amount of torque has been applied to the set screw.
A further complication with set-screw-type lead connector arrangements is that after tightening, the set screw must be sealed from bodily fluids which could cause corrosion or short-circuiting of the connector top or feed through. This sealing is typically accomplished through the use of grommets, which may be damaged during tightening of the set screw.
Several other techniques in the prior art for establishing the electrical and mechanical connection of a lead and an implantable medical device are briefly described in U.S. Pat. No. 4,540,236 to Peers-Trevarton, which patent is hereby incorporated by reference.
Implantable medical devices are typically implanted subcutaneously and may be implanted in a patient for many years. Accordingly, both for cosmetic reasons and for avoiding discomfort and pocket erosion at the implant site, it has always been an objective in the design of implantable devices that the devices be as small and lightweight as possible. In recent years, improvements in various technological fields, particularly those in the field of electronics, have enabled fully-featured implantable devices to be made smaller and smaller. It is believed by the inventors, for example, that a single-chamber demand pacemaker weighing less than five grams, approximately 2.8 centimeters in diameter, and having a volume of approximately 2.5 cubic centimeters is technologically feasible and could soon be commercially available. A conventional connector, even in its smallest practical configuration, would be larger and possibly heavier than an implantable device of such dimensions. The practical limitations on the miniaturization of a connector arise from the fact that the connector's set screws must not be made so small as to become difficult to seat a tool and tighten, or to become insufficiently strong. There are similar limitations on the miniaturization of other types of lead connection structures.
For any type of lead connection which requires a lead terminal to be disposed at the connected end of the lead, the length of the lead is determined at the time of manufacture of the lead, and cannot be changed at the time of implant. Since every patient's anatomy is unique and the implant site of a pacemaker may vary from patient to patient, there is typically some excess length of lead when a fixed-length lead is implanted. Typically, the excess length of lead is gathered together or simply wrapped around the implanted device. This can result in problems such as discomfort to the patient, lead failure due to kinks or bends in the excess length of lead, or displacement of the lead due to forces exerted on the excess length of lead. Additionally, the excess lead wrap may adversely effect the function of activity-based pulse generators by lying across the sensor-carrying face of the generator's housing.
It is believed by the inventors, therefore, that there exists a need for an alternative lead connection arrangement which is readily adaptable to smaller implantable devices. It is also believed by the inventors that it would be advantageous to provide a lead connection arrangement in which the length of the implanted lead can be customized for each patient.